Heat shrinkable coverings for these purposes are currently of two general types. One such covering, as described for example in U.S. Pat. No. 3,297,819 to J. D. Wetmore, comprises essentially a tubular sleeve of heat shrinkable material, typically a crosslinked polymer having an elastic memory, which has been stretched to a dimensionally heat unstable form. In application the tubular sleeve is passed onto the exposed end of the pipe or other article to be covered and is shrunk by the application of heat into close fitting relationship with the article. While this type of covering has the advantage of making a complete and continuous seal around the article, and is not liable to failure except from any inherent weakness in the material of the sleeve, it has certain disdavantages. One obvious disadvantage is that the covering can only be applied if the article to be covered has an exposed end over which the sleeve can be passed. Another disadvantage is that the usefulness of the sleeve is limited to a range of article sizes for which the sleeve diameter is intended. Yet another disadvantage results from the inherent difficulty of extruding sleeves for, say, pipes of large diameter.
The other general type of heat shrinkable covering is represented by the so-called "wrap-around sleeve", one example of which is disclosed in U.S. Pat. No. 4,200,676 to D. A. Caponigro. While wrap-around sleeves are more versatile than tubular sleeves in that they can be readily applied to articles, including large diameter pipes, which do not have an accessible exposed end, the closure systems by which the adjoining ends of the sleeve are interconnected are an inherent source of weakness. Mechanical closure systems are especially vulnerable to damage, while conventionally bonded overlaps can permit slippage during application and subsequently creep due to the hoop stresses remaining in the shrunk sleeves and so render the sleeves less effective than those which have a continuous covering.